Lignosulfonate additive-containing carbon black compositions

ABSTRACT

A carbon black composition comprising carbon black and a lignin dispersant prepared by the steps of methylolating a lignin compound by reaction of less than about 2 moles formaldehyde per 1,000 grams of the lignin, and sulfonating the methylolated lignin by reaction from about 2.5 to 3.5 moles of the sulfite or bisulfite compound per 1,000 grams of lignin at an initial reaction pH of below about 6.6 and at a temperature of at least about 170° C., while allowing the pH of the reaction mixture to rise to a final pH of greater than 7.5 to sequentially sulfomethylate the aromatic nucleus and sulfonate the side chain of the lignin.

The present invention is directed to employing a sulfonated lignin foruse as an additive in chemical compositions and processes, and, moreparticularly, to such sulfonated lignin products suited for use as adispersant, especially in carbon black compositions, to provide lowerviscosities and improved shelf life for such compositions.

BACKGROUND OF THE INVENTION

Lignin products are widely employed as additives in various chemicalprocesses and compositions. Lignin is a complex, high-molecular weightpolymer occurring naturally in close association with cellulose inplants and trees. In the paper-making industry, lignin may be recoveredas a by-product of the cellulose product by two principal wood-pulpingprocesses known as the sulfite process and the kraft process. In thesulfite process, lignin is solubilized from the cellulosic portion ofthe wood pulp by direct sulfonation, while the kraft process is based onan alkaline degradation mechanism causing cleavage of β-aryl etherlinkages in the polymeric lignin which sequentially result in chemicalfunctions of the phenolic and carboxylic type. Kraft process ligningenerally is isolated by acid precipitation from the black liquor of thepulping process at a pH below the pKa of the phenolic groups.

Depending on conditions under which a kraft lignin is precipitated, thelignin may be either in the form of a free acid lignin or a lignin salt.If the lignin is-precipitated at a high pH, such as about 9.5 to 10, thelignin is obtained in the form of a salt. If this lignin is furtherprocessed by washing, acidifying to a low pH, and further washed to besubstantially free of salt and ash-forming ingredients, free acidlignin, known as "A" lignin, is obtained.

The high degree of chemical activity characteristic of lignin permitsthe preparation of many organic derivatives. Lignin by-productsvariously are employed in other chemical compositions as a surfactant,extender, dispersant, reinforcement, absorbent, binder, sequesteringagent, emulsifier, emulsion stabilizer, and stabilizing and protectivecolloid. Lignosulfonate compounds, particularly sodium salts oflignosulfonates, are widely employed as additives and dispersants intextile dyestuffs and printing pigments, and sodium salt sulfonatedlignin by-products have been sold for many years under the trademarksPolyfon® and REAX® by Westvaco Corporation of North Charleston, S.C.

Dilling U. S. Pat. No. 4,590,262 owned by Westvaco Corporation disclosesan improved method of producing sodium salts of lowelectrolyte-containing lignosulfonates suited for use as dye and printpaste additives comprising the steps of ionizing the phenol component ofthe lignin material in an alkaline liquid medium, methylolating theionized phenol component of the lignin by addition of an aldehyde, suchas formaldehyde, lowering the pH of the liquid medium to an acid pH toprecipitate the methylolated lignin material, washing the precipitatedlignin material with water to remove inorganic salts and residualreactants therefrom, and subsequently sulfonating the washed purifiedmethylolated lignin material with a sodium salt of asulfur-oxygen-containing compound, such as sodium bisulfite.

Under processing conditions described in U.S. Pat. No. 4,590,262, usingthe molar amounts of formaldehyde and the sodium-oxygen-containingcompound (sodium bisulfite) described, sulfonation of the lignin occursat the methylolation site on the aromatic phenolic ring of the ligninmolecule, which is referred to as sulfomethylation of the lignin. Asstated, the sulfomethylation reaction preferably is conducted atatmospheric pressure and at a temperature at around 80°-100° C.,although elevated pressures and temperatures above to about 190.C., maybe employed.

U.S. Pat. No. 4,590,262 also discloses that it is possible to sulfonatethe lignin side chain of the aromatic nucleus by sodium sulfitetreatment in the absence of formaldehyde. Low sulfonated lignin productsof the invention of U.S. Pat. No. 4,590,262, i.e., sodium salts ofsulfomethylated lignins having a degree of organically bound sulfonationof about 1 mole or less per 1,000 grams of lignin may be produced, andhigher sulfomethylated lignin products, i.e., having a sulfomethylationof greater than about 1.6 moles per 1,000 grams of lignin, may also beproduced.

OBJECTS OF THE PRESENT INVENTION

It is an object of the present invention to provide a sulfonated ligninfor use as an additive in chemical processes and compositions which isprepared under controlled processing conditions to sulfomethylate thephenolic nucleus and sulfonate the lignin side chain of the ligninmolecule.

It is another object to provide an improved method of producingsulfonated lignin products particularly suited for use as dispersantsand additives in dyestuffs, such as disperse and vat dyestuffs, toproduce lower viscosity dyestuff formulations having improved grindingand shelf life properties.

It is another object to provide an improved method of producingsulfonated lignins having utility as a dispersant in carbon blackcompositions and exhibiting lower viscosity suited for use in grindingoperations with the carbon black and during carbon black storage ofdisperse liquid carbon black systems.

It is a further object to provide an improved dyestuff compositioncontaining as a dispersant therein the sulfonated lignin products of thepresent invention.

It is still another object to provide an improved carbon blackcomposition having as a dispersant therein the sulfonated ligninproducts of the present invention.

BRIEF SUMMARY OF THE INVENTION

The product of the present invention is produced by methylolation andsulfonation of a lignin composition. The reaction is controlled to allowthe pH during sulfonation at elevated temperature to drift from slightlyacidic to slightly alkaline during which time sequentialsulfomethylation of the phenolic nucleus and sulfonation of the ligninside chain of the lignin molecule occurs. More specifically, a lignin,as may be recovered from the black liquor of a kraft paper-makingprocess, is methylolated in aqueous medium at an alkaline pH, e. g.,9.5-12, by reaction with no more than about 2 moles formaldehyde per1,000 grams of lignin, the methylolated lignin is acidified to an acidpH, e.g., a pH of about 5.5, and the methylolated lignin is sulfonatedby reaction with from about 2.5 to 3.5 moles of a sulfite or bisulfitecompound per 1000 grams of lignin at an initial reaction pH of belowabout 6.6 and at a reaction temperature of greater than about 170° C. toobtain a final reaction product having pH of greater than about 7.5.

For lowest viscosities and extended shelf-life in dye compositionsincorporating the lignin products of the present invention, it has beenfound that methylolation with from about 1.4 to 1.7 moles formaldehydeand sulfonation with from about 2.7 to 2.9 moles sulfite or bisulfitecompound per 1000 grams of lignin is preferred.

The sulfonated lignin products of the present invention exhibit improvedproperties over those lignin products identified in prior U.S. Pat. No.4,590,262, particularly with respect to its lower viscosity performanceas a dispersant in disperse and vat dyestuff compositions, as well as adispersant in carbon black compositions. As a dispersant in the dyestuffcompositions, shelf life of the dyestuff compositions is improved. Bymaintaining a medium to high degree of sulfonation in the lignin (1.5-2moles sulfur per 1,000 grams lignin organically bound therein),viscosity stability during extended dye liquid storage is improved.Dyestuff composition viscosities of less than about 100 cps can beachieved after extended storage periods.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The improved sulfonated lignin salts of the present invention may beprepared in one manner in accordance with the following laboratoryprocedures.

A known amount of solid lignin recovered from the black liquor of akraft paper-making process in "A" lignin form is slurried to a 25% totalsolids content and the pH of the slurry adjusted to 11 with addition of50% solution of sodium hydroxide. The temperature of the slurry israised to 65°-70° C., and less than about two moles of formaldehyde areadded to the slurry for reaction for two hours to methylolate thelignin. The resulting methylolated lignin slurry is acidified to a pH ofabout 5.5 by addition of sulfur dioxide gas (SO₂) resulting in areaction creating approximately 1.9 moles of sodium bisulfite per 1,000grams of the lignin. An additional amount of sodium sulfite or sodiumbisulfite is added to the slurry, with pH adjustment with a small amountof sodium hydroxide, to obtain a pH of 6.3 and a total sulfite/bisulfiteconcentration of approximately 2.5-3.5 moles per 1,000 grams of themethylolated lignin.

The methylolated lignin slurry containing the reactive sulfonationingredients is heated at a temperature of above about 170° C.,preferably 175° C., for 1/2 to 4 hours to sequentially sulfomethylatethe phenolic nucleus of the lignin and sulfonate the lignin side chainof the lignin molecule as the pH of the reaction rises to obtain a finallignin composition pH of greater than about 7.5.

The reaction occurring during the method of the present invention may beexpressed by the following chemical equation: ##STR1##

A number of sulfonated lignin salts prepared from various "A" ligninkraft process by-products by the method of the present invention werecombined as dispersants in disperse dye and vat dye formulations andtested for heat stability and dye storage performance. Heat stabilityand dye storage performance of the dye formulations containing lignindispersants of the present invention were compared with dye formulationscontaining lignosulfonate salt dispersants prepared in accordance withthe teachings of U.S. Pat. No. 4,590,262 (prior art).

To obtain heat stability measurements, dye/lignin compositions wereprepared from the lignin products of the prior art and the presentinvention. Compositions containing 50 grams of dyestuff, 35 grams of theparticular sulfomethylated lignin, 125 milliliters of water, and 5 dropsof ethylenediaminetetraacetic acid (1% solids at pH 10.0-10.5) wereadjusted to pH 8.0 with acetic acid. Each dye composition containing alignin additive was ground in a ball mill to the point where the filtertest for disperse dyes was passed. To 1 gram of each solid dyecomposition was added 250 milliliters of water, the pH adjusted to 5.0with sulfuric acid after which the solution was boiled for fifteenminutes, and then filtered through a tared Whatman filter paper no. 2above a no. 4 paper (with vacuum). This test is an adaptation of thestandard American Association of Textile Chemists and Colorists (AATCC)heat stability test. The filter paper was dried, and the residual dyematerial remaining on the filter was calculated by weight and visuallyobserved.

                                      TABLE I                                     __________________________________________________________________________    The Effect of Reaction pH During Dispersant Processing on Heat Stability      and Dye Storage Performance of                                                A Double Strength C. I. Disperse Blue 79 Liquid Formulation                                  CH.sub.2 O/Sulfite or                                                                              Dye Viscosity                                                                         Heat Stability                                   Bisulfite Ratio (Moles per                                                                 Final Product                                                                         in cps after                                                                          (Dye Residue                                     1,000 grams Lignin)                                                                        pH      7 Days  in grams)                         __________________________________________________________________________    Prior Art Lignin 1                                                                           2/3.5        6.2     300     0.0039                            Prior Art Lignin 2                                                                           2/3.5        7.4     140     0.0047                            Lignin of the Present Invention                                                              2/3.5        8.8     80      0.0040                            Prior Art Lignin 1                                                                           2/3.5        4.8     gel (1st day)                                                                         0.0095                            Prior Art Lignin 2                                                                           2/3.5        7.9     348     0.0053                            Lignin of the Present Invention                                                              2/3.5        9.4     140     0.0031                            __________________________________________________________________________

The data presented in Table I provide a comparison of dye compositionscontaining lignin dispersants prepared as in the prior art and lignindispersants prepared as in the present invention. The data show lowercomparative viscosities for the dye compositions utilizing the lignindispersants of the present invention.

The following specific example illustrates the method of preparation ofthe products of the present invention.

EXAMPLE I

The pH of a 20% water slurry of an "A" lignin (recovered from a kraftblack liquor) with an ash content of less than about 1.5% was adjustedwith sodium hydroxide to a pH of 10.8-11.1. The pH adjustment requiredabout 2.3 moles (92 pounds) of sodium hydroxide. After heating thelignin solution to about 68.5°-70° C. (155°-158° F.), two moles (60grams) of formaldehyde are added and the temperature is maintained fortwo hours to methylolate the lignin. 1.9 moles (122 grams) sulfurdioxide gas is introduced quickly into the slurry resulting inacidification of the slurry to a pH of approximately 5.6. To bring thetotal reactive sulfur level to 2.9 moles, 1 mole (126 grams) of sodiumsulfite is stirred into the reaction mixture to raise the pH to around6.0-6.3. Upon final pH adjustment to 6.3, the slurry in an autoclavevessel is rapidly heated to 175° C. and the temperature maintained fortwo hours. Cooling is initiated thereafter and the sulfonated lignincooled as quickly as possible. The final pH of the product may varybetween about 8.4-9.5.

Five "A" lignin by-product samples from black liquors of kraft pulpingprocesses were methylolated and sulfonated, utilizing varying amounts offormaldehyde and sodium sulfite or bisulfite, and at varying conditionsof temperature and pH. These sulfonated products were incorporated asdispersants in disperse dyes. The disperse dye compositions containingthe lignins were tested for initial viscosity and for viscosity afterseven days shelf life. Specifically, dyestuff compositions containing150 grams C. I. Blue 79 dye, 32 grams lignin dispersant, and 273 gramswater were ground to a particle size range below 1 micron, and theirviscosity was measured at 40% solids at a pH of 7.5 to 8. Dyestuffcompositions containing 100 grams of C. I. Vat Black 25 dye, 41.6 gramsof the lignin dispersant, 66.5 grams of glycerin, and 211 grams waterwere ground to a particle size range of below 1 micron, and theviscosity measured at 26% solids at a pH of 7.5 to 8.

Results of the various tests utilizing the various lignin dispersantsare set forth in the following tables.

                                      TABLE II                                    __________________________________________________________________________    Comparison of Dyestuff Composition Viscosity with Sulfonated Lignin           Dispersants of                                                                Varying Sulfite or Bisulfite Content in Sulfonation Step                      Methylolation with 2 moles per 1,000 grams Lignin Temperature of              sulfonation 175° C.                                                    Sulfonation: Moles                Viscosity (cps)                             Lignin                                                                              Sulfite/Bisulfite Compound  Blue 79   Vat Black 25                      Sample No.                                                                          per 1,000 Grams Lignin                                                                      Starting pH                                                                           Final pH                                                                            Initial                                                                            7 Days                                                                             Initial                                                                            7 Days                       __________________________________________________________________________    1     4.0           6.29    9.29  25   165  20   40                                 3.5           6.30    9.25  20   70   20   20                                 3.1           6.30    9.23  18   40   15   20                                 2.9           6.25    9.13  20   35   25   20                                 2.7           6.30    8.95  20   42   15   17                                 2.5           6.32    8.86  25   55   20   20                                 2.0           6.30    8.80  35   360  25   95                           2     3.8           6.35    9.40  20   60                                           3.5           6.30    9.30  18   45                                           3.1           6.30    9.23  20   44                                           2.7           6.32    9.30  20   22                                     3     3.5           6.23    9.15  20   140                                          3.1           6.30    9.26  20   80                                           2.9           6.30    9.20  19   43                                     4     3.5           6.28    9.30  19   44                                           3.1           6.25    8.60  18   38                                           2.7           6.30    8.55  20   21                                     5     3.1           6.05    7.00  30   163                                          2.7           6.00    7.10  35   230                                          2.5           6.10    6.60  40   3125                                   __________________________________________________________________________

As can be seen from the data in Table II (Samples 1-4), lignins in whichthe reactive sulfite or bisulfite content for sulfonation is betweenabout 2.5 to 3.5 moles per 1,000 grams lignin provide dyestuffcomposition viscosities generally below about 100 cps, even after sevendays of shelf storage life. Conversely, if the moles of reactive sulfiteor bisulfite for sulfonation are outside these ranges for the C. I. Blue79 dye composition (first and last runs of Lignin Sample 1), theviscosities are not as low. Similarly, where the final pH of thecompositions are not at least about 7.5 or greater (Lignin Sample 5),higher viscosities occur in the dye compositions.

Seven samples of a "A" lignin by-product of a kraft pulping process weremethylolated and sulfonated utilizing varying amounts of formaldehydeand sodium sulfite or bisulfite for the methylolation and sulfonationsteps, respectively, with sulfonation reaction being carried out atvarying conditions of temperature. The samples were employed as adispersant in a C.I. Disperse Blue 79 dye compositions and viscositiesof the dye/dispersant composition measured at the time of initialpreparation and after seven days shelf life. Results of theseformulations and tests are presented in Table III.

                  TABLE III                                                       ______________________________________                                        Moles  Moles Sulfite                                                          CH.sub.2 O                                                                           or Bisulfite                                                           per 1,000                                                                            per 1,000  Start-             Viscosity (cps)                          Grams  Grams      ing     Final                                                                              Temp. Blue 79                                  Lignin Lignin     pH      pH   (°C.)                                                                        Initial                                                                             7 Days                             ______________________________________                                        1.7    2.9        6.30    8.60 100   650   Gel                                2.0    2.9        6.29    8.60 100   1350  Gel                                2.0    3.5        6.27    8.50 140   35.0  850                                2.0    3.5        6.30    8.65 160   27.5  296                                2.0    3.5        6.44    8.70 175   25.0  45                                 2.0    3.5        6.30    8.65 180   20.0  60                                 2.0    3.5        6.35    8.75 190   20.0  98                                 ______________________________________                                    

From the data presented in Table III, it can be seen that sulfonatedlignins prepared at sulfonation reaction temperatures below about 170°,when employed as dispersants in dyestuffs, do not provide extended shelflife viscosities below 100, whereas those in which the temperature isabove about 170°, e.g., 175° and greater, provide dyestuff dispersantviscosities below 100 cps after seven days shelf life.

Samples of an "A" lignin by-product of a kraft pulping process weresulfomethylated utilizing varying amounts of formaldehyde in themethylolation step. The samples were then employed as dispersants in aC.I. Disperse Blue 79 dye composition, and the viscosities of thecomposition measured after initial formulation and after seven daysshelf life. The results are presented in Table IV.

                  TABLE IV                                                        ______________________________________                                        2.9 Moles Sulfite/Bisulfite per 1,000 Grams Lignin                            Temperature 175° C.                                                    Moles CH.sub.2 O                                                              per 1,000                  Viscosity (cps)                                    Grams                      Blue 79                                            Lignin    Starting pH                                                                              Final pH  Initial                                                                              7 Days                                  ______________________________________                                        4.0       6.20       8.90      1650   Gel                                     3.5       6.17       8.60      590    Gel                                     3.0       6.22       8.55      410    8900                                    2.5       6.14       8.40      75     405                                     2.0       6.20       8.36      20     45                                      1.7       6.10       8.31      20     18                                      1.4       6.13       8.38      16     16                                      1.1       6.14       8.32      18     25                                      0.8       6.21       8.41      17     32                                      0.5       6.18       8.07      20     33                                      0.2       6.19       8.02      20     107                                     --        7.28       10.01     209    Gel                                     (Reaction without CH.sub.2 O occurs at Starting pH of 7.28 or                 ______________________________________                                        above)                                                                    

From the data presented in Table IV, it can be seen that sulfonatedlignins prepared with more than about 2 moles formaldehyde in themethylolation step did not provide the desired low viscosities indyestuff dispersions, whereas those which use 2 moles or lessformaldehyde do provide the desired lower viscosity in the dyestuffdispersions.

Products of the present invention were combined with and employed as adispersant in carbon black suspensions, and the results of testsconducted thereon with respect to comparisons with other dispersants arelisted in Table V.

Carbon black dispersions were prepared utilizing the followingformulation:

    ______________________________________                                               7/2.0 g         Carbon Black                                                  4.4 g           Dispersant                                                    4.3 g           NH.sub.4 OH                                                   119.3 g         H.sub.2 O - distilled                                         200.0 g         Total                                                  ______________________________________                                    

                                      TABLE V                                     __________________________________________________________________________                    Grinding pH                                                                           Final %                                                                            Particle                                                                           Viscosity.sup.(a) (cps)                     Dispersant      Initial                                                                           Final                                                                             Solids                                                                             Size Initial                                                                           Week 1                                                                             Week 2                                                                             Week 3                                                                             Week                     __________________________________________________________________________                                                         4                        MARASPERSE CB OS/3                                                                            10.0                                                                              10.1                                                                              38.2 0.21 1420                                                                              2550 2560 3100 3500                     (sulfite lignin manufactured                                                  by Lignosol Corp. of Canada)                                                  Sulfonated lignin prepared by                                                                 10.0                                                                              10.0                                                                              38.2 0.22 1570                                                                              2480 2930 3570 3860                     method of the present invention                                               Sulfonated lignin prepared by                                                                 7.9 7.9 38.2 0.23 1650                                                                              2260 2790 3540 3650                     method of the present invention                                               __________________________________________________________________________     .sup.(a) ViscositiesBrookfield, Spindle #2 at 100 rpm.                   

As can be seen from the Table V, the viscosities of the carbonblack/lignin dispersions prepared in accordance with the presentinvention compared favorably in viscosity at an initial and weeklyperiods of up to four weeks with Marasperse CB, which is a consideredstandard in the industry.

That which is claimed is:
 1. A carbon black composition comprisingcarbon black and a sulfonated lignin dispersant prepared bymethylolating a lignin material by reaction less than about 2 molesformaldehyde per 1,000 grams of the lignin and sulfonating themethylolated lignin by reaction with from about 2.3 to about 3.5 molesof a sulfite or bisulfite compound per 1,000 grams of the lignin at aninitial reaction pH of below about 6.6 and at a temperature of about170° C., allowing the reaction pH to rise to a final pH greater than 7.5to sequentially sulfonate both the methylolated aromatic nucleus and aside chain of the lignin.
 2. A composition as defined in claim 1 whereinthe lignin is methylolated with from about 1.4 to 1.7 moles formaldehydeper 1,000 grams of lignin, and the methylolated lignin is reacted with acomposition containing from about 2.7 to 2.9 moles of sulfite orbisulfite compound per 1,000 grams of lignin at a pH of between about6.1 to 6.3.
 3. A composition as defined in claim 1 wherein the finallignin composition has an organically bound sulfur content of greaterthan about 1.5 moles per 1,000 gram moles of lignin.
 4. A composition asdefined in claim 2 wherein the lignin is methylolated at a pH of about11, the pH of the methylolated lignin is lowered to an acid pH byaddition of sulfur dioxide, and sodium sulfite or sodium bisulfite isadded for the sulfonation reaction.